When most micrometeorites enter Earth’s atmosphere at hyperspeed, fifty times the speed of a rifle bullet, they melt by frictional heat. During the subsequent deceleration, the temperature lowers and recrystallization occurs. To trigger crystallization in a molten rock, something must start it, a nucleus. This is usually some metal or other dense element. From there, crystallization grows in the amorphous (glass) melt, which is frequently seen in glass (V-type) micrometeorites. Like Photo #1.
There is an analogy to this, which can be observed directly, in freezing soap bubbles. Crystallization is triggered by the snow crystals on the ground, and crystals start to grow in the still liquid water. In front of the crystalline border between the growing crystalline area and the still amorphous glass, small isolated “snow crystals” appear. If allowed to grow, these crystals may end up as individual crystal domains, which is a characteristic feature of many micrometeorites. In stripy barred olivine (BO-type) micrometeorites we usually see areas of different stripy orientation. These started to grow as isolated crystals in the original melt. Four of the glass micrometeorites in figure 1 have small isolated pyramidal crystals growing in the glass. The Atlas of Micrometeorites describes this phenomenon as The Soap Bubble Effect.
On soap bubbles, the growth of the crystals is like on a two-dimensional surface. But how does this phenomenon translate for micrometeorites? Is it on the surface of the micrometeoroid, or also inside, in three dimensions? This has been an open question, until now. Today Jan Braly Kihle and I present the first documentation of this, a World première:
Micrometeorite NMM 2583 (see Photo #2) is an icon which is known to many stardust fans. The photo has been printed in prestigious magazines and exhibited in art galleries. In fact, before we launched our debut fine art collection, several people contacted me because they wished to display this exotic micrometeorite in their home.
Measuring approximately 0.7 mm, NMM 2583 is a giant stone droplet from Space where the thick end is crystalline and the tail is composed of amorphous glass. The color is deep brown. In the black and white image from the scanning electron microscope (SEM, see Photo #4), we can see how crystallization has been initiated by small metal beads in the front, which then grew backwards. At one point, the temperature must have dropped below solidification, reaching the freezing point, and the long tail has remained glassy, only rounded by surface tension.
With our new photo technique, Jan and I have a glimpse of the inside of the little Space rock. A small light source directly from behind shines through the translucent glass, making it possible for us to see small independent olivine crystals growing ahead of the major crystalline front. Not only on the surface but as a three-dimensional pattern inside the glass matrix (see Photos #5 and 6). This has never been documented before, and we are proud to share it with you. Enjoy!
By popular demand, the large hi-res color photo of the beautiful micrometeorite, NMM 2583, is now available as part of our debut limited edition fine art collection, so you can have stardust on your wall.
Stay tuned for another blog article here at Project Stardust investigating the obvious follow-up question: How was did NMM 2583 form in the first place? So, hang on, more stardust discoveries are coming up soon!